1. Field of the Invention
The invention relates generally to a DVD data processing system and method, and more particularly to a DVD EDC (Error Detection Code) check system and method in which the EDC check of a sector may be performed without prior descrambling the sector.
2. Description of the Related Art
DVD (Digital Versatile Disk) disk is a newly developed medium to record data. The DVD disk with single side and single layer can store up to 4.7 GB (Giga Bytes) of data, which is about seven times of data possibly stored in a CD disk. Compared to the CD disk, the DVD disk has higher storage capacity by storing data in smaller pits along narrower tracks. Also, by using a more sophisticated sector encoding technology, the DVD disk has higher capacity than the CD disk. The data format and data encoding technology of the DVD disk are different from and more complex than those of the CD disk. Thus, the data processing and error detecting operations are also different when reproducing data stored in the DVD disk.
Please refer to FIG. 1, which shows a conventional DVD data processing system for reproducing data stored in the DVD disk. The DVD data processing system includes an optical pickup 12, a digital converter 14, a sync code detector and 8/16 demodulator 16, a DVD sector decoder 18, a buffer memory 20, a host interface 24 and a host interface bus 22. The optical pickup 12 reads data by irradiating light to the DVD disk 10 and senses the variation of the reflected light on the disc surface. Then, the digital converter 14 generates a channel bit stream of amplified and digitized waveform. Next, the sync code detector and 8/16 demodulator 16 detects a sync and demodulates the channel bit stream, and converts the channel bit stream into a plurality of sectors. The sectors are then transferred to the DVD sector decoder 18 for error correction (by error correction code ECC), descrambling, and error detection (by error detection code EDC). In addition, a buffer memory 20 is provided for storing temporary data generated during the operation. If the error correction and error detection are successfully performed and there's no error found in the sector, the sector will be descrambled and transferred to the host interface bus 22 such as an IDE bus through the host interface 24.
Both the CD disk and the DVD disk are general-purpose data storage media. The CD disk may use different formats for storing data, depending on whether audio, video, or other types of data is to be stored, while the DVD disk uses only one format to store data. FIG. 2 illustrates the format of a DVD sector without ECC parity information. It is noted that since ECC is not directly related to the present invention and is well known in the art, the ECC operation will not be described for the sake of brevity. As shown in FIG. 2, each DVD sector includes four bytes of ID (sector identification), two bytes of IED (ID Error Detection), six bytes of CPR_MAI (Copyright Management Information), 2,048 bytes of main data, and four bytes of EDC (error correction code). The four-byte ID (sector identification) indicates the logical sector address of the DVD sector. The ID (sector identification) and the IED (Identification data Error Detection) together can be used to form a (6, 4) Reed-Solomon code, which can be decoded to detect and correct the error(s) in the ID. The six-byte CPR_MAI (Copyright Management Information) are reserved for copyright protection. The four-byte EDC is calculated using checksum, cyclic redundancy check (CRC) codes or the like. The EDC will be added to the 2,060 bytes of ID, IED, CPR_MAI and main data. The calculation of the EDC is described in the following. Assuming that the MSB of the first byte of ID is b16511 and the LSB of the last byte of EDC is b0, the four-byte EDC is chosen so as to make the polynomial I(x) be exactly divided by the check polynomial g(x), as shown below.I(x)=b16511x16511+b16510x16510+ . . . +b2x2+b1x+b0g(x)=x32+x31+x4+1  (1)
It is noted that the check polynomial g(x) in the DVD format is different from the EDC check polynomial in the CD format.
When data are recorded onto the DVD disk, the EDC is calculated and then added to the ID, IED, CPR-MAI, main data, and form a sector. Then the main data is scrambled. In other words, the EDC is calculated based on the un-scrambled main data. Therefore, in the conventional art when data are read from the DVD disk, the sector data is prior descrambled, and then the EDC check is performed. In general, the method for decoding the sector includes the procedures of descrambling the main data, then calculating and checking the EDC. FIG. 3 shows a conventional DVD data decoding procedure. As shown in FIG. 3, when the decoder receives the sector, the 2048 bytes of main data are prior descrambled. Thereafter, the EDC check unit performs the EDC calculation and check the 2064 bytes of data in the sector. If the calculated EDC value equals to zero, it indicates that the sector does not have errors and a sector-correct signal is generated. If the calculated EDC value does not equal to zero, it indicates the sector has errors and a sector-error signal is generated.
In the conventional art as shown in FIG. 3, the descrambling procedure is performed only for the purpose of the EDC calculation and check process. Therefore, at this stage the descrambled data is not used for other purposes. For example, in the conventional art, at this stage the descrambled data is not transferred to the host interface bus. Therefore, if the EDC calculation and check processes for the sector can be performed directly without the prior descrambling procedure, the processing speed in the decoding process may be improved, and the hardware resources may be more-efficiently used.